I put the mast under the pulpit as well. On my Triad trailer, that puts the top of the pulpit at about 13'2" I believe overpasses are supposed to be at least 13'6" and newer ones are at least 14'. Look out for older ones that may be shorter and also for signs and other things that stick out over the side of the road. When I get my boat home for the winter, I usually have a few branches I collected along the way.
As far as securing the mast, It is lashed under the pulpit, supported by a 4x4 that goes through the partners and sits on the mast step (corners need to be chamfered to fit in step) wih a U shaped plywood support on top. Then I have a second wooden support that spans the footwell just aft of the traveller and holds the mast above the companionway. This position allows you to still drive the boat with the mast down as required in the Chicago river or other places. My two supports were blatantley copied from John MacArthur from Smiles.
I found that strapping the mast down to the deck tended to put pressure on the cabin top next to the companionway flexing it enough so that it was almost impossible to remove the companionway sliders. I've also found that skying all the halyards (or putting in messengers) and taking off the shrouds, forestay and spreaders makes the mast easier to tie down. To wrap up all of the halyard tails, get a wide roll of saran wrap from a shipping department and wrap them before you pull the mast. You may not want to leave it on all winter though because it does collect some moisture.
